Treatment of slag



Patented Mar. 2l, 1933 UNETED STATES PATENT OFFICE TRACY BJLRTHOLOM'YEW, 0F PITTSBURGH, PENNSYLVANIA TREATMENT 0F 'SLAG Application mea June 4, 192s. serial No. :massil The resent invention relates to the treatment ci) slag, and more especially to the agitation of a molten slag containlng gases in supersaturated solution, whereby a foamlike cellular sla structure may beV produced, although modi cations ofthe treatment may produce either a dense or a spongy structure. The invention also relates to the structure produced by such a treatment and to the apparatus for carrying out the process. Some technicians 'consider as in slag as adsorbed rather than as disso ved, and in describing the gases as being in solution in the slag, I intend to include thereby gases whether adsorbed or dissolved.

The molten slag containing gases in solution is stirred or agitated, whereby the gases which exist in a state of supersaturated solution in the slag at the temperature at which it is stirred are coalesced into gas bubbles in the slag. The slag is preferably so cooled under controlled temperature conditions that it is given a viscosity sufficient to hold the bubbles in the molten viscous or plastic lslag so that a solidified'foam or cellular structure results. If the temperature conditions are so controlled that the slag is suiiciently Huid. so that the bubbles formed from the gas released from its supersaturated solution can escape from the slag, the resultant product can be made dense and substantially free from contained gas bubbles. By varying the temperature conditions it is possible to produce a product varying from a light foam or cellular structure, through a heavier cellular structure to a dense structure without gas pockets.

My process lends itself particularly to the production of 'slag for building blocks or brickswhich have light weight, structural strength, high resistance to penetration of moisture, and good heat and sound insulating qualities, and which are specially adapted for use in modern building construction, and particularly in steel frame buildings where a building material of this class is desired.

ln the accompanying drawing,-

Figure l is an elevation partly in section -of the invention,

The

Figure 2 is a detail view' and carrying out my of the stirrer;

. Figure 3 is a perspective .view of a light foam-like slag block by the process.

The process will now such as can be produced be described with particular reference to the apparatus illustrated in the drawing, it being understood, however, that th e process may be carried out with other forms of apparatus.

Referring reference in which container cates a container 1s treated. The

to the illustrated embodiment numeral 1 indithe` molten slag comprises a circular shell 2 closed on the sides and open at the to for the rece ell 2 has anc tending inwardly to gealed slag from turning The container is closed at tion of the molten slag. oring projections 2a exhold the body of conor being lifted. the bottom by a plate 3 having a central opening 4 through which the treated slag may be discharged.

The container is heat insulated with suitable heat insulating-.material 5.

provided for 1n the container hollow water cooled tube 7, helically wound a strip 8. also provided with arms per opening of the contain and throw out any tending to choke the inlet.

A. stirrer 6 is stirring or agitating the slag l. The stirrer comprises a around which is The stirrer 1s 9 and l0 at the uper 1 to break up slag' crusts or material A guard l1 having a discharge chute 12 preferably surrounds the u container to catch flying spattered slag. The stirrer laterally projecting arms pper part of the any surplus material thrown out by the arms 9 and 10, or any lower end of the rod is also preferably provided with 13 and a downwardly projecting cruciform iin 14# to assist in keeping the discharge opening ci. clear. The lower end of the rod has a circular pla-te l5 which normally closes the opening e when the rod is in its lowered position.

The stirrer rod 7 is continuously rotated through bevel gearing 16 source of power, such as shaft 17. The cooling w from a suitable the belt driven ater is supplied through the stirrer rod by an internal pipe 18, which projects to the bottom of the which is shown as not rotated.

ater 1s supplied to the inner pipe 18 through the flexible hose connection 19 and is discharged through the flexible hose conconnected to the upper art of the rotating circular stirrer rod 7 t rough the rotatable water fitting 21.

The stirrer 7 is arranged to be vertically reciprocated to intermittently discharge the slag from the container l, by means of the lever 22, driven by crank 23 and connected to the rod 7 at 24.

The molten slag is preferably tapped from the blast furnace into a transfer and storage ladle or receptacle from which it is poured into the container l through the chute 25. In addition to this, a-chute 26 is desired to admix other materials with the slag.

charged in aistream 27 into the upper part of the receptacle. The slag tends to freeze against the shell 2, forming an outer solidied slag layer 28. It also tends to freeze against the stirrer 7, forming an inner slag layer 29, which will have the general contour of a helical screw following the helically wound strip 8. Between the rotating inner slag body 29 and the outer. containing slag body 28, the molten slag passes down as the stream 30. It will be understood, of course, that there is no sharply defined dividing line between the solidified slag and the molten slag, but that they merge into each' other. As the slag 30 passes downwardly by gravity and also by the screw action of the helix 8, it is Subjectedy to stirring or agitation which is produced by the slippage between the contiguous concentric layers of the slag around the stirrer.

The stirrer rod 7 is given an up and down movement, being drawn upwardly from the position shown in the drawing and then forced downwardly. lI his serves to intermittently eject the viscous or even plastic molten slag from the bottom of the receptacle.

The slag as it is formed in a blast furnace 1s under the internal blast furnace pressure, usually in the neighborhood of about fifteen pounds to the square inch above that of the atmosphere. Because of this super-atmospheric pressure, the slag in the furnace can hold in solution more gas than at atmospheric pressure. When the slag is discharged from the furnace into a ladle in which it is quiescent, the gases do not escape readily from the molten slag but exist in a state of super-saturation. The stirring of the slag, however, permits the coalescence of the excess gas held in the' super-saturated solution into bubbles which form little gas pockets in the'viscousslag.

The tendency of a liquid to hold gas in super-saturated solution and the release of such gas by stirring is illustrated in the commonly observed phenomenon of stirring a glass of carbonated Water or bevera e, such as ginger ale, ring results in the formatlon of carbon gas which existed 1n a state of super-saturatedsolution in the water.

As the slag Hows downwardly through the agitator it 1s cooled and thereby rendered more viscous. .The viscosity of the slag tends to hold the bubbles in the body of the slag as small gas pockets and prevents heir escape to the surrounding atmosphere or coalescence into large size gas pockets. By controlling the cooling of the slag so that it is in a rather thick viscous or lastic condition as it reaches the bottom ci) the agitawith a spoon, which stirtor, enough ofthe gas, which 'is released from l its state of yby productlon under a hlgher pressure t an that present in the foainer, as in a normal blast furnace operation, my experience indicates that it is possible to foam with this apparatus a slag which is not so initially supersaturated with gas. Molten slag not supersaturated with gas at higher pressure than that maintained in the foamer, or by forming or melting the slag at a temperature materially higher than that of the slag in the foamer, or both.

In Figure 3 is illustrated a. small slag block as produced by this process. The block consists of a continuous body of slag which contains small bubbles or gas ckets, as shown in the drawing. A n ana ysis of the gas which is contained in the gas pockets shows about 80% nitrogen and about 15% carbon monoxide when using blast furnace slag, showing that the gas bubbles are formed by the gas which was in solution in the slag inthe blast furnace. These as pockets are substantially uniformly distributed through the material, the material being dist' ished by its homogeneous structure and a sence of large gas pockets. The size -of the gas pockets can be controlled by the amount of stirring and by the temperature. In a typical example, the greater part of the gas pockets averaged between about oneeighth and one-sixteenth of an inch 1n diameter.

The solidified sla which forms the continuous phase in t e gas-slag dispersion, forms continuous lms or walls surrounding and sealing the gas pockets, so that while the material has a foam-like cellular structure, it is not pervious to water. A brick of the material ma be thrown into a bucket of water and w1ll iloat indefinitely. The water resisting properties of the material particularly adapts it for blocks or bricks in bullding construction.

The high and uniformly distributed voids in the material give it a high heat insulating value, which also adapts it for building material.

The weight per unit volume of -the product depends upon the amount of gas retained in bubbles in the material, and this amount can be regulated by controlling the tem erature and therefore the viscosity and bu bleholding capacity of the slag as it leaves the apparatus. v

The amount of gas which is released and retained in the material, and consequently the Weight per unit volume ofthe material, may be regulated by the amount of gas held in a state of supersaturation in the slag as itis treated in the agitator, and the temperature control of the slag which regulates its viscosity and consequent ability to hold the gas bubbles.

l have found that the amounty of supersaturation naturally aiorded by blast furnace pressures gives an ample amount of gas which can be released during agitation. lf such slag is run into the agitator and cooled in the agitator so as to be discharged in a rather thick viscous condition, aconsiderable part of 'the released gas may be retained in the slag and a light weight foamlilre cellular structure produced. On the other hand, if the cooling during agitation is insuflicient to develop such viscosity, the gas which is released by the stirring of the slag can escape from the fluid slag and a dense structure containing substantially no voids or gas pockets can be produced.

The viscosity of the slag may be controlled by varying the input. if the rate -to the cubic foot, since this gives suilicient of yin ut is lrelatively Smau the viscosity increased, whereas .by relatively -largein ut of highly heated slag the Aviscosity o the slag as it passes through. the

a itator and is dischar e may be decreased.

T e viscosit of the s ag may also be oontrolled by t e chilling action accomplished by the addition through the chute 26 of cold material, for example fine cold slag in the form of slag meal or granulate. By varying the amount of this admixture the tem erature and viscosit of the discharged pro uct may be contro led. Liquids may be added, if desired, to control the temperature. Where the quantity of slag discharged is to be maintained fairly constant the regulation of temperature and viscosity is preferably obtaired by such additions. Where the output' need not'be constant, regulation of the viscosity may be controlled by varying the feed of the slag into the apparatus.

By suitably controlling the viscosity of the slag as it is stirred to form the as bubbles, the weight per unit volume o the resultant product can be controlled. A material canAbe made as light as 15 lbs. to the cubic foot, or as dense as 180 lbs. to the cubic foot. The preferred weight is about 40 lbs.

a5 slag in the block for structural strength and at the sam time suilic'ient gas is held to form a lig t cellular structure, having the general appearance of the block shown in igure 3 of the drawing.

While for building materials it is preferred to form the cellular structure with unbroken walls between the gas ockets so as to render it impervious tov moisture, the intercellular partitions may be partly broken down to form a porous structurre suitable for filter material. This may be done by prolonging the cooling of the slag during agitation until the viscosity of the slag is increased to a point where the walls be- 11g tween the gas pockets are-broken down by their surface tension under the agitation.

It will therefore be seen that by suitable temperature control the character of the product may be greatl varied. For examgie, if the slag is hel in a Huid condition uring agitation so that the gas bubbles can escape, a dense product may be produced. As the viscosity is increased by suitably controlled and lowered tempera- 320 tures, the amount of gas bubbles may be increased to produce a block of increased lightness, but having continuous enclosing walls around the gas pockets. As the temperature is still further decreased during agitation these walls may be caused to be ruptured, producing a spongy structure which is pervious to ii uids.

The product is uni orm or homogenous,

that is to say, the gas pockets will average 30;

to be of the same order of size and lthe material is remarkably free from large gas kets. Any excess uantity of gas or arge bubbles develope during the early stages of the agitation can pass up through the more liquid charge at the top of the agitator and out to the atmosphere. The stirring or kneadin movement to which the slag is subjecte as it passes downwardly through the agitator serves to thoroughl mix and knead to ether the slag, thus ten ing to produce t e uniform homogeneous product.

The elimination of gas from the slag by the agitating treatment, even when no -bubbles are retained, facilitates casting of the slag. Normal blast furnace slags give products which, immediately after casting and during solidification of their interiors, swell, deform and even disrupt, spewing 'out foamy slag from their interiors. The agitating treatment, whether bubbles are retained or not, tends to obviate this swellin and thereby obviates or minimizes the de ormation and swelling in the cast products.

While I have described the process with particular reference tothe illustrated embodiment of the a paratus, it will be apparent that other Forms of apparatus may be employed to agit-ate or stir the slag to -release the gas under properly controlled temperature and viscosity conditions, and

y that the invention is therefore not limited to the particular apparatus employed.

While blast furnace slag is tapped from the blast furnace ispreferred as the molten' slag material, because it can be readily obtained at a low cost and because it inherently has available an adequate amount of gas held in supersaturated solution, other slags may be employed, either natural furnace slags or artificially prepared slags, and it is therefore to be understood that the term slag vis intended as a term of general delinition and not of limitation, and to include Various materials which may be artificially made and having the characteristics of slag.

While the preferred embodiment of the invention and the process of treating slag have been specifically described, it is to be understood that the invention may be otherwise embodied and practiced within the sco of the following claims.

claim:

1. The process of treating molten slag containing a gas in supersaturated solution, which comprises agitating the slag to release the contained gas to form a foam, and retaining at least a part of the gas during the setting of the slag to form a foam-like cellular structure.

2. The process of treating molten slag containing a gas, which comprises agitating the molten slag to produce gas bubbles Athereasomar molten slag, while cooling it to a viscosity sufficient to retain at least a part of the gas bubbles in the slag to form a foam.

3. The process of treating molten sla containing gases in solution therein, whic comprises releasing the gases held in solution in the slag to form gas bubbles therein, while cooling it under regulated temperature conditions so .as to form a homogeneous solid foam.

4. The process of forming a solid foamlike cellular slag structure, which comprises melting slag under pressure so as to form in the slag a gaseous solution supersaturated at atmospheric pressure, and agitating the molten slag at atmospheric pressure while cooling it to a viscous condition so as to liberate the gas from its supersaturated solution and form gas bubbles which are retained in the solidified slag.

5. The process of forming a solid foamlike cellular slag structure, which comprises forming a gas-containing molten slag under pressure, and thereafter agitating the slag under a lower pressure while cooling so as to liberate the gas from its solution and form bubbles which are retained in the viscous body of the slag as it congeals.

6. The process of forming a solid foamlike cellular slag structure from blast furnace slag, which comprises forming the slag in a blast furnace at a super-atmospheric A pressure in the usual manner, whereby the slag upon discharge from the furnace contains gases in supersaturated solution at atmospheric pressure, removing the slag from the blast furnace, and thereafter agitating the molten slag at substantially atmospheric pressure while cooling it to a viscous condition so as to liberate the gas from its supersaturated solution and form gas bubbles which are retained in the solidified slag.

7. The process of forming molded porous foam-like cellular'slag articles from blast furnace slag, which comprises taking the slag from the blast furnace wherein the slag is formed under a superatmosphericfpressure, continuously agitating a flowing stream of such slag containing gases in a supersaturated solution so as to liberate the gases and form gas bubbles while simultaneously cooling the stream of slagto render it sufficiently viscous to retain at least a part of the thus-formed gas bubbles thereby to form a liquid or viscous foam, and casting such foam in molds.

8. The process of producting a porous cellular material from molten slag, which comprises continuously leading into an agitator a molten slag containing dissolved gases and subjecting the molten slag to agitation therein to release the gases while simultaneously cooling the slag to a condi- Leonesa part of the released gases to form a viscous 0am, removing the viscous foam from the agitator, and cooling the same to solidification, whereby served.

9. The proce of treating molten slag containing a gas in supersaturated solution, which comprises agitating the slag in the absence of a substantial amount of moisture to release the contained gas to form a foam,

and retaining at least a part of the gas during the setting of the slag to form a foamlike cellular structure.

10. The process of treating molten slag containing a gas in solution, which comprises ag'itating the molten slag in the absence of a substantial amount of moisture to produce gas bubbles therein from the gas initially contained in the molten slag, while cooling it to a viscosity suicientto retain at least a part of the gas bubbles in the slag' to form a foam.

. l1. The process of forming a solid foamlike cellular slag structure, which comprises forming a gas containing molten slag under pressure, and thereafter agitating the sla under a lower pressure and in the absence o a substantial amount of moisture while cooling it so as to liberate the gas from its solution and form bubbles which are re` body of theslag as it tained in the viscous congeals.

12. The process of formin a'solid foamlike cellular slag structure rom blast` furnace slag, which comprises forming the slag in a blast furnace at a superatmospheric pressure in the usual manner, whereby the slag upon discharge from the tains gases in supersaturated solution at atmospheric pressure, removing the sla from the blast furnace, and thereafter agltating the molten slag in the absence of a substantial amount of moisture and at substantially atmospheric pressure while cooling it to a viscous condition so as to liberate the gas from its supersaturated solution and form s bubbles which are retained in the solidi ed slag.

In testimony whereof I have hereunto set my hand.

TRACY BARTHOLOMEW.

the foam structure is pre` 

